Earth's New 'Quasi' Moon Will Stick Around for Centuries

Astronomers have detected a small asteroid that doesn’t seem to want to go away. Called a quasi-satellite, this new companion circles around the Earth as it orbits the sun — and it’s going to stay that way for the next few hundred years.

Technically speaking, this newly discovered asteroid, dubbed 2016 HO3, is in orbit around the sun. But as it makes this annual trek, it’s also circling around the Earth. It’s far too distant to be considered a true natural satellite of our planet, but it’s a good example of a quasi-satellite, or near-Earth companion.

This little guy, which measures somewhere between 40-100 metres across, never ventures too far from Earth. As it orbits the sun, asteroid 2016 HO3 spends about half of the time closer to the sun than Earth, and passes ahead of our planet; the other half of the time it falls behind.

It’s also in a tilted orbit, which causes it to weave up and down on the orbital plane like a bob on choppy waters. As NASA’s Paul Chodas put it in a press statement, “[i]n effect, this small asteroid is caught in a little dance with Earth.”

Over the course of many years, the asteroid starts to drift inwards and outwards, but Earth’s gravity is strong enough to ensure that its new companion doesn’t venture too close or too far. It never gets further than about 100 times the distance of the Earth to the Moon, and never closer than about 38 times the distance of the moon, or about nine million miles (14 million km). So it’s not a threat to our planet.

Asteroid 2016 HO3 was detected in late April by the Pan-STARRS 1 asteroid survey telescope in Hawaii. Calculations suggest that the asteroid became a quasi-satellite about a hundred years ago, and that it’ll stick around for centuries to come.

Seeing as that’s the case, can we please give it a better name than 2016 HO3? [NASA]